FIG. 1 illustrates a conventional processing system 10. The processing system 10 includes a plurality of host computers 12A-12C. Each of the host computers 12A-12C is coupled to an I/O channel 14. The I/O channel 14, in turn, is coupled to a control unit (CU) 16. The CU 16 is coupled to a storage medium such as a disk array 18. As is well known, a processing system could include a plurality of CU 16s. 
The control unit CU 16 has a large cache 17 that is used to cache data being accessed by one or more host computers 12A-12C. Typically each of the host computers 12A-12C attempts to access the CU 16. The CU 16 does not have any knowledge of objects or files; it only understands blocks, tracks and cylinders. In addition, all types of data have the same importance to the CU 16. For example, data that belongs to a database index of the CU 16 does not have a different importance relative to the data that is pointed to by the index itself.
It is important for response time in the processing system 10 that data be resident in the cache 17. It is well known that data can be retrieved more quickly from the cache 17 than from the disk array. In order to decide which data to keep in the cache 17, CUs currently use the Least Recently Used (LRU) algorithm 19. That is, the least recently used data is discarded from the buffer 17 periodically. There is also a variation to handle sequential access. When sequential access is detected, data ahead of the access is pre-fetched, while data that has already been accessed is immediately discarded.
In the last few years, it has been clearly shown by experience, when caching data on the host computer, that certain objects are significantly more important than others. A typical example is that indices are significantly more important than data. The net result is that caching should not only be based on what has been accessed most recently, but also on the type of data being accessed to improve the processing system performance. As has been previously described in conventional systems the CU 16 has no information about the type of data being accessed.
Accordingly, what is needed is a system and method for improving the overall response time of the transaction systems using a host computer within a processing system by ensuring that important data is cached constantly. The present invention addresses such a need.